1. Field of the Invention
The present invention relates to a suspension system for vehicles. In particular, it relates to a suspension system for vehicles that includes: a torsion bar; a suspension arm which is supported to a vehicle body end (i.e. to an end of a vehicle body, as it collectively means an adequate number of integral parts of the vehicle body and an adequate number of rigid members fixed relative to the vehicle body, as used herein) through a bush member; and a coupling structure for coupling the torsion bar to the suspension arm. The invention is addressed to an improvement of the coupling structure.
2. Description of Relevant Art
There are illustrated various examples of conventional suspension systems at pages 56-59 in Vol. 11 of JIDOUSHA KOUGAKU ZENSHO (a complete book of automobile engineering) published from KABUSHIKI KAISHA (a corporation) SANKAIDO, Japan, on Aug. 20, 1980.
In the Accompanying Drawings, FIG. 1 shows a typical conventional independent suspension system applicable to a right front wheel of an automobile.
This conventional suspension system includes a torsion bar 11 employed as a suspension spring member. Further, it has a combination of an upper arm 1 and a lower arm 3 as a pair of suspension arms shaped in wishbone forms and arranged in a vertically opposing manner.
The upper and lower arms 1 and 3 are each shaped in a wishbone form. They are both vertically swingable. When installed in a vehicle, they extend substantially horizontally, i.e. in a longitudinal direction L and a transverse direction T of the vehicle. In the figure, designated by reference characters Lf and Lr are forward and rearward senses of the longitudinal direction L, respectively, and Ti and To are inward and outward senses of the transverse direction T, respectively.
The arms 1 and 3 have their transversely inner portions longitudinally bifurcated into front fixing parts 5b and 7b and rear fixing parts 5a and 7a. The front and rear fixing parts 5b, 7b and 5a, 7a are each supported to a vehicle body end through a corresponding unshown pivotal bush member. An unshown single upper link spindle is inserted at both ends thereof into unshown upper link bushes fitted in the front and rear fixing parts 5b, 5a of the upper arm 1. The arms 1 and 3 have their transversely outer portions 5c and 7c provided with unshown upper and lower ball joints, respectively, which ball joints cooperate with each other for rotatably supporting an unshown steering knuckle member to thereby support an unshown road wheel.
A shock absorber 9, which is connected at an upper end 9a thereof to a vehicle body end, is pivoted at a lower end 9b thereof on a bolt 50a fastened to a bracket 50 on a transversely intermediate portion of the lower arm 3.
The torsion bar 11 has a serrated front end part 11a coupled to the rear fixing part 7a of the lower arm 3, and a serrated rear end part 11b fixed to a vehicle body end.
FIG. 2 shows in plan a coupling structure between the torsion bar 11 and the lower arm 3.
The rear fixing part 7a of the lower arm 3 is further bifurcated in the longitudinal direction L to have a pair of front and rear projections 7d and 7e extending in the inward sense Ti. The front projection 7d comprises a transversely extending vertical wall 7f, which is bent at a lower edge thereof in the forward sense Lf to provide a narrow horizontal flange 7g and at an upper edge thereof in the rearward sense Lr to be joined to a horizontal top wall 7j of the lower arm 3. The vertical wall 7f of the front projection 7d constitutes part of a forwardly curved front side wall 7k of the rear fixing part 7a of the lower arm 3. Likewise, the rear projection 7e comprises a transversely extending vertical wall 7h, which is bent at a lower edge thereof in the rearward sense Lr to provide a narrow horizontal flange 7i and at an upper edge thereof in the forward sense Lf to be joined to the top wall 7j of the lower arm 3. The vertical wall 7h of the rear projection 7e constitutes part of a forwardly curved rear side wall 27 of the rear fixing part 7a.
The vertical walls 7f and 7h of the front and rear projections 7d and 7e are interconnected to each other at their transversely intermediate parts by a longitudinally extending spindle 13, which is inserted therethrough in the forward sense Lf from outside the rear projection wall 7h (see FIG. 1) and fastened thereto with a nut. The spindle 13 is coupled through an unshown bush member to a vehicle body end. The spindle 13 has at its rear end a serrated head part 13a facing a rear outside of the wall 7h of the rear projection 7e.
The rear outside of the wall 7h provides a mount place for a butterfly-like torque-bearing joint member 15 called "torque arm".
The torque arm 15 comprises a longitudinally extending cylindrical hollow part 15c, a first wing 15a as an integral arm part extending in the outward sense To, and a second wing 15b as an integral arm part extending in the inward sense Ti. The first wing 15a is offset in the rearward sense Lr relative to the second wing 15b, so that a significant gap is left between a front face of the first wing 15a and a curved outside of the rear side wall 27 of the rear fixing part 7a, when the torque arm 15 is set in position.
The torque arm 15 is fixed to the rear fixing part 7a of the lower arm 3, using a relatively long first bolt 17 and an associated nut 19 for fastening the first wing 15a and a relatively short second bolt 23 and an associated nut 25 for fastening the second wing 15b. The second bolt 23 may be paired.
The first bolt 17 is inserted in the rearward sense Lr from ahead of the front side wall 7k of the rear fixing part 7a, through a torque arm collar 21 and a thru-hole formed in the first wing 15a.
The torque arm collar 21 is provided through the rear fixing part 7a of the lower arm 3, extending in parallel to the spindle 13. The collar 21 is welded to be fixed to the lower arm 3. A rear part 21a of the collar 21 protrudes outside the rear side wall 27 of the rear fixing part 7a, and has a rear end face 21b formed as an abutment surface for the fastening of the first wing 15a.
As the first bolt 17 is inserted through the collar 21 and tightened by the nut 19, the first wing 15a of the torque arm 15 is fastened against the end face 21b of the collar 21.
The second wing 15b of the torque arm 15 is securely fastened to the rear projection 7e, by the second bolt 23 tightened with the nut 25.
The use of torque arm collar 21 ensures a fastened fixing of the torque arm 15 by the provision of a fastening oriented surface (21b) between the first wing 15a of the torque arm 15 and the rear side wall 27 of the fixing part 7a of the lower arm 3. The rear side wall 27 is curved, as the lower arm 3 has a restricted configuration in relation to the road wheel. A secured fastening of the torque arm 15 to the lower arm 3 is thus permitted by the torque arm collar 21.
In the torque arm 15, the hollow part 1 5c is serrated at a front end thereof for an anti-rotational coupling with the head part 13a of the spindle 13 and at a rear end thereof for an anti-rotational coupling with the front end part 11a of the torsion bar 11. The respective anti-rotational coupling may be otherwise achieved.
The front end part 11a of the torsion bar 11 is concentrically aligned to a pivotal axis of the spindle 13, so that the torsion bar 11 is twisted by the torque arm 15 relative to a vehicle body end, i.e. between both end parts 11a and 11b thereof, when the lower arm 3 is caused to vertically swing about the pivotal axis, together with the torque arm 15. The torsion bar 11 thus effectively functions as a suspension spring member.
The conventional suspension system described however employs a multiplicity of component parts, with a reduced efficiency of assembly work and a needed high processing accuracy notwithstanding an associated increase in accuracy of assembly subjected to an unavoidable limitation.
In other words, in the conventional structure, the torque arm 15 is assembled to the lower arm 3 by using the first bolt 17 inserted in the collar 21. The torque arm 15 is thus assembled with an accuracy subjected to a fixing error of the collar 21 relative to the lower arm 3 and a fitting error between the collar 21 and the first bolt 17, in addition to a fixing error of the spindle 13 relative to the lower arm 3. The accuracy in assembly of the torque arm 15 depends on a total of such errors.
To reduce the total of such errors, one may minimize the fixing error of the spindle 13 relative to the lower arm 3. This measure however needs an increased accuracy in processing holes for fixing the spindle 13 in the lower arm 3. The processing will be complicated.
The fixing holes for spindle 13 may be successfully processed with an increased accuracy. However, a resultant structure is still subject to a reduced accuracy due to a clearance between the first bolt 17 and the collar 21. It is limited for the assembly accuracy to be increased with a reduced total of errors.
The conventional structure needs additional work for the torque arm 15 to be fastened with the first bolt 17 fitted in the collar 21 and tightened with the nut 19. The assembly efficiency is reduced by the multiplicity of component parts.